Pyrophosphatase mechanism: We plan to 1) locate specifically modified amino acid residues at the active site within the primary sequence of PPase, which should be of great importance in evaluating the forthcoming results of X-ray crystallography studies, 2) establish, using paramagnetic and fluorescent probes, the disposition of metal ion with respect to substrate at the active site of PPase, and the disposition of strongly and weakly bound metal ions with respect to each other, 3) study using these same probes, conformational changes in PPase arising from incubation with ZN2 ion and the lag process preceeding the steady state for Zn2 ion -ATPase and possibly Co2 ion -PPase and Mn2 ion -PPase as well and 4) synthesize and study the PPase catalyzed hydrolysis of inorganic pyrophosphorthioate in order to distinguish between SN1(P) and SN2(P) mechanisms for PPase. Adenylate affinity labels: We plan to synthesize photolabile derivatives of adenosine, AMP, ADP and ATP and use them to identify a variety of biological receptors, particularly the ADP receptor in blood platelets.